To satisfy demands for wireless data traffic having increased since commercialization of 4th-Generation (4G) communication systems, efforts have been made to develop improved 5th-Generation (5G) communication systems or pre-5G communication systems. For this reason, the 5G communication system or the pre-5G communication system is also called a beyond-4G-network communication system or a post-long-term evolution (LTE) system.
To achieve a high data rate, implementation of the 5G communication system in an ultra-high frequency (mmWave) band (e.g., a 60 GHz band) is under consideration. In the 5G communication system, beamforming, massive multi-input multi-output (MIMO), full dimensional MIMO (FD-MIMO), an array antenna, analog beamforming, and large-scale antenna technologies have been discussed to alleviate a propagation path loss and to increase a propagation distance in the ultra-high frequency band.
For system network improvement, in the 5G communication system, techniques such as an evolved small cell, an advanced small cell, a cloud radio access network (RAN), an ultra-dense network, a device to device (D2D) communication, a wireless backhaul, a moving network, cooperative communication, coordinated multi-points (CoMPs), and interference cancellation have been developed.
In the 5G system, advanced coding modulation (ACM) schemes including hybrid frequency-shift keying (FSK) and quadrature amplitude modulation (QAM) modulation (FQAM) and sliding window superposition coding (SWSC), and advanced access schemes including filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) have been developed.
Meanwhile, a full-duplex communication system using a full-duplex communication scheme is an innovative system capable of doubling a channel capacity by simultaneously performing transmission and reception using the same frequency resource. The full-duplex communication system may not be able to avoid self-interference (SI) caused by a transmitted signal received back due to bidirectional communication, and research has been continuously carried out to solve a problem occurring due to SI.
A scheme which has recently attracted the most attention cancels an influence of SI in terms of a circuit, and the SI cancellation scheme is divided into a digital cancellation scheme using digital signal processing and an analog cancellation scheme using an analog interference cancellation circuit depending on whether a magnitude of an SI signal causing SI is within or out of a dynamic range in which the SI signal may be received in a digital manner. Typically, to cancel SI at a system level, the digital interference cancellation scheme and the analog interference cancellation scheme may be generally used at the same time.
The digital interference cancellation scheme detects channel characteristics, by using a signal branched from a digital transmission signal and a digital reception signal, from a difference between the transmission signal and the reception signal, and applies the detected channel characteristics to the digital reception signal to cancel the SI signal.
The analog interference cancellation scheme cancels the SI signal from a received signal by applying a circuit having gain adjustment, phase adjustment, and a fixed delay time to a transmission signal branched from an analog transmission circuit, based on an assumption that a received SI signal is a finite number of signals received after an already known fixed time delay. The gain and the phase to be adjusted by the circuit are obtained from estimated interference characteristics.
However, the performance limitation of the analog interference cancellation scheme and the digital interference cancellation scheme is determined by hardware configurations, and for high output power, desired SI cancellation performance may not be satisfied merely by the analog interference cancellation scheme and the digital interference cancellation scheme. To overcome such limitations, a scheme for separating a transmission antenna and a reception antenna or a scheme for using polarization characteristics of the transmission and reception antennas has been considered. However, the scheme for separating the transmission antenna and the reception antenna may increase the size of an apparatus in which the antennas are mounted or complicate installation of the antennas, and the scheme for using the polarization characteristics of the transmission and reception antennas may not effectively cancel the SI signal caused by reflection.
Therefore, a need exists for a scheme for cancelling the SI signal in a full-duplex communication system, other than the scheme for separating the transmission antenna and the reception antenna or the scheme for using polarization characteristics of the transmission and reception antennas.
The above data is presented as background data only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.